1. Field of the Invention.
This invention relates generally to electronic devices, and more particularly to a mid and far infrared to near infrared light converter using InAs self-assembled quantum dots.
2. Description of Related Art.
Advances in the field of electronics have brought new means for the detection and use of infrared radiation in the mid-and far-infrared regions. The use of semiconductor materials has made the detection of infrared radiation more efficient and cost efficient. Even more compact and efficient means of detection and imaging in the infrared region of the spectrum can be devised using new semiconductor structures.
Large two-dimensional focal plane arrays in the mid- and far-infrared (MandFIR) region have important applications in the fields of pollution detection, thermal imaging, and imaging of astronomical objects. A typical approach for detecting MandFIR radiation uses indium antimonide (InSb) or mercury cadmium telluride (HgCdTe) detector arrays bonded to a silicon (Si) chip for multiplexing. However, this approach suffers because the difference in material thermal expansion coefficients makes it difficult to bond the detectors to the Si chip. Further, processing of HgCdTe or InSb is itself extremely complex and costly.
An alternative route has been the development of semiconductor quantum well infrared photodetectors (QWIP). More recently, QWIPs have been integrated to light emitting diodes (LEDs) and other electronics to produce a visible signal out of an infrared source. However, QWIPs have also fallen short of cheaply providing a reliable device because QWIPs are insensitive to normal incident light. The inter-sub-band transitions in a quantum well (QW) under normal illumination are forbidden due to selection rules for quantum wells. To avoid this problem in QWIPs, additional devices, such as special optics or surface gratings, are required to prevent normal illumination incident on the QWIP. Further, large lateral diffusion of photoexcited carriers in the QW deteriorate the spatial resolution of the QWIP imaging device. From the foregoing, it can be seen then that there is a need in the art for inexpensive, easily producible MandFIR detectors that can accept normal illumination.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and device for light conversion. The proposed devices convert the signal from an IR or MIR source into a visible or near visible signal or image. This method of conversion is called upconversion since it converts low energy IR photons into visible or near visible photons.
The method comprises the steps of exciting an electron in a quantum dot with an incident photon having the first wavelength, typically in the infrared or near infrared range of the spectrum, the excited electron having a first energy, tunneling the excited electron through a barrier into a stress induced quantum dot, and recombining the excited electron with a hole in the stress induced quantum dot, therein producing a photon having a second energy and the second wavelength, typically in the visible or near visible range of the spectrum. The strain induced quantum dots may be replaced by another quantum dot with the appropriate dimensions.
The device comprises a substrate, a spacer layer, coupled to the substrate, a second layer, coupled to the spacer layer, wherein the second layer comprises a different material than the spacer layer, a third layer, coupled to the second layer, wherein the third layer comprises at least one quantum dot, a fourth layer, coupled to the third layer, comprising a quantum well corresponding to each quantum dot in the third layer, a fifth layer, coupled to the fourth layer, wherein the fourth layer and fifth layer comprise a strain induced quantum dot corresponding to each quantum dot in the third layer; and a sixth layer, coupled to the fifth layer, the substrate and the sixth layer for contacting the device. The quantum well layer may also be replaced by a layer of quantum dots.
Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples in accordance with the invention.